The Energy Balance Phenotpying Core provides services to the members ofthe NYORC and to other eligible investigators. These services include consultation, assessment of energy intake, energy expenditure, and body composition. The Core is actively engaged in phenotyping mouse and rat models of obesity and is in a unique position to provide the stated services. The development of obesity in animal models is dependent on hyperphagia; exaniples are leptin and leptin receptor deficient rodents. The hyperphagia is dependent on influences from the hypothalamus, as targeted ablation of neuropeptide expression partially corrects this defect in ingestive behavior. Two of the NYORC Cores, Energy Balance Phenotyping and the Molecular Biology/Molecular Genetics Core, have done a series of ontogenetic studies to correlate the onset of hyperphagia with overexpression of a hypothalamic neuropeptide, NPY. The Molecular Biology/Molecular Genetics Core provided the breeders and the genotyping assays to determine gene dosage for leptin receptor mutation which the Energy Balance Phenotyping Core performed measures of caloric intake. These studies provided a temporal relationship between over-expression of an orexigenic peptide and hyperphagia, consistent with the hypothesis that increased activity of NPY neurons is partly responsible for the obesity/diabetes syndrome of leptin and leptin receptor deficiency. This type of collaboration between investigators in the Molecular Biology/Molecular Genetics core and the Energy Balance Phenotyping core are expected to continue and expand over the next 5 years of investigation. The collective experience ofthe Core's staff provides a broad range of expertise in ingestive behavior, metabolic physiology and body composition.